The present invention relates to hermetically sealed compressor assemblies. More particularly, the present invention relates to hermetically sealed compressor assemblies having a shell which is staked in place in a unique manner to resist excessive axial and circumferential loading.
Hermetically sealed motor compressors of various designs are well known in the art. These designs include both the piston/cylinder types and scroll types. While the present invention applies equally well to all of the various designs of motor compressor units, it will be described for exemplary purposes embodied in a hermetically sealed scroll type fluid machine.
A scroll type fluid machine has a compressor section and an electrical motor section mounted in a hermetic shell with fluid passages being formed through the walls of the hermetic shell. The fluid passages are normally connected through pipes to external equipment such as, for example, an evaporator and condenser when the machine is used in a refrigeration system.
The scroll type compressor section has a compressor which is comprised of a non-orbiting scroll member which is mated with an orbiting scroll member. These scroll members have spiral wraps formed in conformity with a curve usually close to an involute curve so as to protrude upright from end plates. These scroll members are assembled together such that their wraps mesh with each other to form therebetween compression chambers. The volumes of these compression chambers are progressively changed in response to an oebital movement of the orbiting scroll member. A fluid suction port communicates with a portion of the non-orbiting scroll member near the radially outer end of the outermost compression chamber, while a fluid discharge port opens in the portion of the non-orbiting scroll member close to the center thereof. An Oldham's ring mechanism is placed between the orbiting scroll member and the non-orbiting scroll member so as to prevent the orbiting scroll member from rotating about its own axis.
The non-orbiting scroll member is secured to the main bearing housing by means of a plurality of bolts extending therebetween which allow limited relative axial movement between the bearing housing and the non-orbiting scroll member. The attachment for the non-orbiting scroll member is more fully disclosed in assignee's copending application Ser. No. 07/591,444 entitled "Non-Orbiting Scroll Mounting Arrangements for a Scroll Machine" filed Oct. 1, 1990, the disclosure of which is hereby incorporated herein by reference.
The orbiting scroll member is driven by a crankshaft so as to produce an orbiting movement with respect to the stationary scroll member. Consequently, the volumes of the previously mentioned chambers are progressively decreased to compress the fluid confined in these chambers, and the compressed fluid is discharged from the discharge port as the compression chambers are brought into communication with the discharge port. The housing is fixedly attached to the hermetic shell. The attachment methods for connecting the housing to the hermetic shell include bolting, pin or plug welding and/or press or shrink fitting. While each of these methods offer certain advantages, they also come with individual disadvantages.
The press or shrink fit is the least expensive attachment method and it is capable of withstanding most of the forces normally generated by the assembly. The compressor assembly is capable, however, under certain conditions, of generating forces which could exceed the holding capabilities of the press fit design. When these excessive forces are generated, the housing could slip either axially or circumferentially with respect to the hermetic shell, adversely affecting the operation of the compressor assembly.
Welding of the housing resolves the issues of being able to withstand the forces in excess of the normal, but the cost of producing a welded assembly in volume production is relatively high.
Bolting the housing to the shell will also resolve the issue of being able to withstand the forces in excess of normal, but the cost involved in preparing both the shell and the internal components to be able to accommodate a bolt and still maintain the necessary hermetic seal makes the technique unsuitable to volume production. In addition, the problems of properly completing the fastening operation and the costs associated with the fastener make this an undesirable option.
Accordingly, what is needed is a means of fixedly attaching the housing of a motor compressor unit to the hermetic shell which is capable of withstanding both the normal and the abnormal forces generated during the operation of the compressor. The means of fixedly attaching the housing should be both inexpensive and reliable, and suitable for high volume production.